1. Field of the Invention
The present invention relates to an active element array structure. More particularly, the present invention relates to an active element array structure for an optically self-compensated birefringence liquid crystal display capable of twisting of liquid crystal molecules from a splay state to a bend state rapidly.
2. Description of the Related Art
Rapid progress in semiconductor devices and man-machine interface products has lead to a proliferation of multi-media systems in our society. In the past, cathode ray tube (CRT) has dominated the market because of its price and superb quality. Although the conventional CRT has many advantages, the design of the electron gun renders it heavy and is a potential source of radiation. With big leaps in the techniques in manufacturing semiconductor devices and optical devices, thin film transistor (TFT) liquid crystal displays (LCD) have gradually become main-stream display products. This is because a TFT LCD has an exceptional picture quality, a high spatial utilization and a low power consumption and provides a radiation-free environment.
In general, liquid crystal displays can be classified according to the liquid crystal type, the driving method and the positioning of the light source. The OCB (optically self-compensated birefringence) LCD is one type of LCD having a rapid response speed suitable for displaying a succession of rapidly changing pictures in an animation show or broadcasting movies through a computer. The OCB also stands for Optically Compensated Bend, and Optically Compensated Birefringence respectively. However, before the optically self-compensated birefringence liquid crystal display can be used for the rapid display of pictures, the liquid crystal molecules within the display must first be transited from a splay state to a bend state.
FIG. 1A is a schematic view showing the liquid crystal molecules inside a conventional optically self-compensated birefringence liquid crystal display in a splay state. FIG. 1B is a schematic view showing the liquid crystal molecules inside a conventional optically self-compensated birefringence liquid crystal display in a bend state. As shown in FIGS. 1A and 1B, the optically self-compensated birefringence liquid crystal molecules 100 are positioned between a top substrate 110 and a bottom substrate 120. The top substrate 110 and the bottom substrate 120 both have an alignment layer with rubbing direction parallel to each other. Before the optically self-compensated birefringence liquid crystal molecules 100 are subjected to an electric field, the liquid crystal molecules are aligned in a splay state. Prior to using the optically self-compensated birefringence liquid crystal display, the liquid crystal molecules 100 must be activated to an idling state through an electric field applied in a direction perpendicular to the top substrate 110. In other words, the liquid crystal molecules 100 must be transited into a bend state. Before the pixel of a conventional optically self-compensated birefringence liquid crystal display can be driven normally, a few minutes must be set aside for the transition of the liquid crystal molecules from the splay state to the bend state. That means, a long warm up period is required before the display is in an idle state. However, instant operation is essential for any type of display. Hence, an optically self-compensated birefringence liquid crystal display must have a fast transition period before it is acceptable to most consumers.
Among the conventional techniques for speeding up the transition, one method uses a special driving method to kick-start the transition. Another method uses a special pixel design to alter the alignment of a portion of the liquid crystal molecules so that the transition from a splay state to a bend state is faster.